It is one of the rarest drops, but there was always one place that it seemed to drop 3-4 of them all together. It was on the big AA battery ramp (number 2?) underneath the residential district. Climb up that, they are at the top. Try at night if they aren't there by day, though there might also be a strong monster up there at night.
help help im being repressed come see the violence inherent in the system